FIG. 1 is a sectional view of a conventional micro gas sensor.
The conventional micro gas sensor comprises: a substrate 110, a membrane 120, a micro heater 130, an insulating layer 140, a sensing electrode 150 and a gas sensing substance 160. After the membrane 120 and the micro heater 130 are sequentially formed on the substrate 110, the insulating layer 140 is formed thereon. The sensing electrode 150 and the gas sensing substance 160 are formed on the insulating layer 140. The micro heater 130 formed on the membrane 120 is formed with an irregular thickness. Consequently, the insulating layer 140 formed in a subsequent process is irregular in thickness by the irregular thickness of the micro heater 130.
When the micro gas sensor having the aforementioned irregular structure is operated at a high temperature for a long time, since materials around the micro heater 130 have different thermal expansion properties, internal stress is generated at the boundary position between the materials and the micro heater 130 by heat. As a result, the insulating layer 140 is broken, causing problems in electrifying the sensing electrode and the micro heater and making it difficult to maintain durability for a long time.
Further, when an array sensor of high density is manufactured by using a nano wire composed of the material, such as SnO2, ZnO or the like, or a nano particle sensing substance, the sensing substance is formed, using a contact printing method. Then, the conventional gas sensor has the problem in that it is difficult to form the sensing substance by the contact printing method due to the irregular surface around the micro heater.